Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$85.41	10.548%	$94.419	$94.42	$94.40	$94.40
Purchase #2	$37.73	3.244%	$38.954	$38.95	$38.95	$39.00
Purchase #3	$151.45	3.339%	$156.5069	$156.51	$156.50	$156.50
Purchase #4	$167.54	13.837%	$190.7225	$190.72	$190.70	$190.70
Purchase #5	$79.45	11.587%	$88.6559	$88.66	$88.65	$88.70
Purchase #6	$123.38	6.494%	$131.3923	$131.39	$131.40	$131.40
Purchase #7	$107.84	11.534%	$120.2783	$120.28	$120.30	$120.30
7 purchase totals =	$752.80		$820.9289	$820.93	$820.90	$821.00